单选题：John opened the door. There ________ he had never seen befo..

Only when the villagers were faced with water shortage___ how serious the problem of water pollution was．A．did they realizeB．will they realizeC．they did realizeD．were they realized

_____ that it was sold out when it came out. [ ]A. So was her successful book B. So successful was her book C. So her book was successful D. So successful her book was

This is an illness that can result in total blindness if_______. A．to leave untreatingB．left untreatedC．leaving untreatingD．is left untreated

He is taller than he______.A．usedB．used to beC．used toD．used to do

All substances, ＿＿＿＿＿ solids, liquids, or gases, are made up of entirely atoms. A．whether theyB．whether C．whether are theyD．whether are